Pitch sustaining means for a key-operated monophonic instrument

ABSTRACT

A pitch sustaining circuit having a sample command circuit and a delay line in parallel which have their inputs connected to the keyboard contact input, a field effect transistor having its source connected to the delay line output, its gate connected to the output of the sample command circuit, and a pitch memory circuit having its input connected to the drain of the field effect transistor and its output connected to a voltage controlled oscillator.

United States Patent Farley et al. 0

[54] PITCH SUSTAINING MEANS FOR A KEY-OPERATED MONOPHONIC INSTRUMENT [72] Inventors: Rene Farley; David O. Rocheleau,

both of Ottawa, Ontario, Canada [73] Assignee: Canadian Patents and Development Limited, Ottawa, Ontario, Canada [22] Filed: Sept. 23, 1971 [21] Appl.No.: 183,097

I52] US. Cl. ..84/1.13, 84/1 .24, 84/126 [51 I Int. Cl. ..G10h 3/00 I58] Field 01 Search ..84/l.01,'l.11,1.07,1.09, 84/1.10,1.24, 1.26

[56] References Cited UNlTED STATES PATENTS 2,879,388 3/1959 George ..84/l.01 X

2,888,849 6/1959 Humphrey et al. .........84/1.01

3,095,466 6/1963 Le Caine ..84/1 .11

[451 Oct. 10,1972

3,180,918 4/1965 l-larmon......................84/1.01 3,288,904 11/1966 George ..84/ l .01 3,516,321 6/l972 Harris ..84/l.26 X 3,524,365 8/1970 Jarvis ..84/1 .01 3,546,353 12/1970 Jenny ..84/ l .01 3,562,395 2/1971 Peterson ..84/l.26 X

Primary Examiner-Lewis H. Myers Assistant Examiner-U. Weldon ArtomeyJames R. Hughes ABSTRACT A pitch sustaining circuit having a sample command circuit and a delay line in parallel which have their inputs connected to the keyboard contact input, a field effect transistor having its source connected to the delay line output, its gate connected to the output of the sample command circuit, and a pitch memory circuit having its input connected to the drain of the field effect transistor and its output connected to a voltage controlled oscillator.

3 Claim, 2 Drawing Figures PITCH SUSTAINING MEANS FOR A KEY- OPERATED MONOPHONIC INSTRUMENT This invention relates to a pitch sustaining system for electronic musical instruments and more particularly for a key-operated monophonic instrument.

in US. Pat. No. 3,095,466 entitled KEYBOARD FOR A MONOPHONIC INSTRUMENT WITH IM- PROVED SOUND-SUSTAINlNG MEANS issued to H. Le Caine on June 25, 1963, the need for a sound sustaining means is discussed and a suitable keyboard and circuit arrangement is described. The system described, however, involves the use of a second (auxiliary) contact on each key of the main keyboard and an extra contact on the auxiliary keyboard plus a relay arrangement for switching a pitch memory circuit into and out of operation. In other words, the auxiliary contacts and the relays are required to transfer the input of a voltage controlled oscillator from the output of the keyboard pitch contact circuit to a memory" circuit or voltage level holding device. The pitch sustaining means shown in the patent works well but requires the use of extra mechanical contacts and relays.

It is therefore an object of the present invention to provide a pitch sustaining means that requires a minimum of mechanical devices.

These and other objects of the invention are achieved by a pitch sustaining circuit having a sample command circuit and a delay line in parallel which have their inputs connected to the keyboard contact output, a field effect transistor having its source connected to the delay line output, its gate connected to the output of the sample command circuit, and a pitch memory circuit having its input connected to the drain of the field effect transistor and its output connected to a voltage controlled oscillator.

ln drawings which illustrate an embodiment of the invention,

FIG. 1 is a block diagram of the system,

FIG. 2 is a more complete circuit diagram giving detail of the sample command circuit, the delay line, and the pitch memory circuit.

Referring to FIG. I, a keyboard It] typically made up of a series of switches (keys) 11 which tap a resistance divider l2 energized from a voltage supply 13 provides a voltage level output related to the highest switch or key closed. It should be noted that if two or more switches are closed at the same time, the voltage level corresponds to that of the highest switch. ln other words it is a monophonic (or one key at a time) keyboard. The output is applied to both a sample command circuit 14 and a delay line 15. The output of the sample command circuit is connected to the gate G of field effect transistor PET and the output of the delay line is connected to the source S. The output of the field effect transistor (drain D) is connected to a pitch memory circuit 16 which in turn is connected to a voltage controlled oscillator (VCO) [7.

In operation, when a key 11 of keyboard is pressed (closed) the sample command circuit 14 operates to close the gate of the FET completing the connection between the delay line and the high impedance circuit (the pitch memory circuit) and on to the VCO. The VCO produces an output voltage having a frequency directly related to the voltage level at its input. Voltage controlled oscillators are known and widely used and their operation need not be described further here. Upon initial make of the keyboard contact, the sample command voltage operates the gate of the FET before the voltage from delay line 15 appears at the source terminal of the FET. When this delayed voltage arrives it is transferred to the drain of the FET and on to the high impedance input of the pitch memory circuit.

When the key is released, the keyboard voltage falls very rapidly and this is detected by the sample command circuit which then operates to open the gate of the FET. This in effect open-circuits the connection between the delay line and the FET drain or high impedance input to the pitch memory circuit. Because of the delay line the voltage at the source terminal does not fall immediately so in effect the gate voltage is removed before the delay line voltage is removed from the drain terminal. Because of the high impedance and high capacitance of the pitch memory circuit it charges up to the voltage of the drain and stays at that voltage because the gate of the FET has opened the connection between the pitch memory circuit and the delay line. Because of the high impedance and high capacitance of the pitch memory circuit, this voltage is held long enough to allow the VCO to oscillate at constant pitch (frequency) while slow delays of the sound level (amplitude) are taking place.

Two effects are involved, that of the delay line which is comparatively short and delays the voltage for a sufficient period to allow the sample command circuit to operate and that of the sample command circuit (sample and hold circuit) which is comparatively long.

Referring to FIG. 2, the delay line, the sample com mand circuit, and the pitch memory circuit are shown in more detail. The input from the keyboard passes through an isolator 18 after which it is applied to both the sample command circuit 20 and delay line 19. The delay line 19 is made up of inverters 21 and 25 and a delay section made up of capacitors C1, C2, and C3 and chokes 22, 23, and 24. The inverters are required to provide convenient voltage levels and polarities in relation to ground. The line gives a voltage time delay of approximately 1 milli-seconds which is of sufiicient duration to allow the sample and command circuit to operate before the voltage passing through the delay line reaches the FET. The sample command circuit 20 includes an inverter 26 and a trigger made up of direct coupled transistors T] and T2 which controls (opens and closes) the gate of the FET. The pitch memory circuit includes an operational amplifier 27 providing a high input impedance and a long time constant section made up of resistor R2 and capacitor C2. The time constant of this circuit is sufficiently long to maintain the input voltage to the VCO at a constant value allowing it to oscillate at constant frequency while decay of the sound is taking place.

The circuit described above has application in various types of electronic music instruments and especially in monophonic keyboard instruments. The circuit requires only one contact for sample command and pitch information and thus eliminates the need for a complete set of contacts plus the relay and contacts which are involved in the pitch memory circuit shown in US. Pat. No. 3,095,466.

What is claimed is:

A pitch sustaining system for electronic musical instrument of the key-operated monophonic type comprising:

. a delay line also connected to the means for providing a voltage level,

i a field effect transistor having its gate electrode connected to the output of the sample command circuit and its source connected to the output of the delay line,

. a pitch memory circuit including a predetermined decay time-constant element having its input connected to the drain of the field effect transistor and providing an output voltage for controlling the frequency of oscillation of a voltage controlled oscillator,

f. the delay time of the delay line being sufficiently long to allow the sample command circuit to turn on the field effect transistor before arrival of the voltage passing through the delay line.

I 2. A pitch sustaining system as in claim I wherein the delay line includes a delay element made up of a series of inductors and capacitors.

3. A pitch sustaining system as in claim I or claim 2 wherein the pitch memory circuit is formed of a resistor and capacitor in parallel connected to an input of resistance feedback operational amplifier. 

1. A pitch sustaining system for electronic musical instrument of the key-operated monophonic type cOmprising: a. means for providing a voltage level related to the closing of one of a set of keys, b. a sample command circuit including a trigger having its input connected to the means for providing a voltage level, c. a delay line also connected to the means for providing a voltage level, d. a field effect transistor having its gate electrode connected to the output of the sample command circuit and its source connected to the output of the delay line, e. a pitch memory circuit including a predetermined decay timeconstant element having its input connected to the drain of the field effect transistor and providing an output voltage for controlling the frequency of oscillation of a voltage controlled oscillator, f. the delay time of the delay line being sufficiently long to allow the sample command circuit to turn on the field effect transistor before arrival of the voltage passing through the delay line.
 2. A pitch sustaining system as in claim 1 wherein the delay line includes a delay element made up of a series of inductors and capacitors.
 3. A pitch sustaining system as in claim 1 or claim 2 wherein the pitch memory circuit is formed of a resistor and capacitor in parallel connected to an input of resistance feedback operational amplifier. 